Reciprocating mechanism for inclined mineral separating pneumatic tables



G. E. SHWCROSSSv RECIPROCATING MECHANISM FOR INCLINED MINERAL sept. 16,1,947.

SEPARATING PNEUMATIC TABLES Filed NOV. 5, 1945 www Patented Sept. 16,`1947 RECIPROCATING MECHANISM FOR IN- CLINED DHNERAL SEPARATING PNEU-MATIC TABLES George E. Shawcross, Fenton, YStoke-on-Trent,

England, assi'gnor of one-half to Saxon Engineering Company, Limited,Staffordshire, England; Lloyds Bank Limited, London, England, executorof said George E. Shawcross, deceased Application November 5, 1945,Serial No. 626,807 In Great Britain November 16, 1944 1 Claim.

. 1 The invention relates mainly to the dry cleaning of coal,particularly of the smaller sizes, but may also be used for the dryseparation of other minerals such as tin ore from gangue. While wetprocesses will produce a satisfactory separation of coal and shale ordirt, the subsequent elimination of the water or other liquid involvesheavy additional expense when small coal is in question. Proposals havebeen made for the dry cleaning of small coal, but no such proposal hasbeen entirely successful in practice in that it provided an output ofshale completely free of coal and of coal without appreciable admixtureof shale.

The usual form of apparatus for the dry cleaning of coal comprises aperforated table set on a slope and oscillated in an oblique directionmaking also an oblique angle with the table. The table is perforated forthe passage of air to keep the bed of raw coal in a floating stateduring treatment, so that the shale may sink to the bottom of the layerand be conveyed to the top end of thetable, while the cleaned coalslides down over the shale to be discharged at the lower end. Thepresent invention relates to apparatus in'accordance with this generaldescription. It is, of course, understood that with other mnerals theheavier constituent is usually the wanted product, but this makes nodifference to the apparatus in question, which always discharges theheavier constituent at the upper end of the table.

According to the invention the apparatus has three features incombination, rstly the direction of oscillation is not the same at bothends, having a larger vertical component at the'lower end, secondlymeans such as discharge weirs are tted at both ends of the activesurface of the table to maintain the depth of material under treatmentat a suitable value, and thirdly the table surface is made rough oruneven in such a manner as to ensure transmission of the conveyingeffect to the material in contact with it.

Other features are desirable for improving the results still further,and these will first be enumerated. The perforations in the table shouldpreferably be small and closely spaced. They may for instance bediameter at 1/2" spacing, giving a perforation area less than 3% of thetable area. The preferred form of the table surface is of serratedlongitudinal section with low steep fronts facing towards the upper endand with the reverse slopes quite gentle. It is then convenient to placea row of holes near the bottom of each dip and a second row part way upthe slope; the next row of holes would then be in the next dip.

Where a very fine fraction of coal or other material is to be treated,such as from 53s" to als", this construction would not be suitable. Afine wire mesh may be used for material of the smaller particle sizes.The natural roughness of the Wire mesh due to the crossings of warp andweft is suflicient for ensuring that the heavier fraction in Contactwith the table has the conveying effect transmitted to it. In fact, itsgreater conveying power will usually necessitate a greater slope of thetable.

Adjustable dampersmay run transversely of the table on its under side tomodify the distribution of air so as to secure the best results. Thesemay be flaps adjustable through a right angle on fixed bars attached tothe table. Usual-i` ly it is desirable to vshut off the air completelyor nearly so for a short distance at the top end and to reduce the airdischarge a little for perhaps a quarter or a fifth of the table lengthat the lower end, but other adjustments may be better vfor certainvarieties of coal.

The discharge Weir at the upper end is preferably made sloping toprovide a gentle ramp over which the shale will glide easily. Such afeature is of less value at the lower end because of the smallerfriction of coal. l

Other features of the invention may be regarded as having the moreimmediate purpose of providing convenience in adjusting the table to thebest operating conditions for whatever material is to be treated.

Either or both of the discharge weirs may be made adjustable in slope orheight or both. It is preferable to set the coal discharge Weir higherthan the shale discharge Weir to equalise the resistance to the'passageof air through the bed, since the heavier shale imposes a greaterresistance than an equally thick layer of coal. For the smaller sizesthe bed may be 1%" thick at the shale end and 21/2 thick at the coalend,` but with larger sizes the depth should be made commensurate withthe size of the pieces of material. Two other adjustments are desirable.One is 3 that of the slope of the table itself and the other is that ofthe directions of oscillation.

The invention is illustrated by a table for the dry cleaning of smallcoal shown in the accompanying drawing, in which Figure 1 is a sideelevation of the whole table, and

Figures v2 and 3 fragmental views in section and plan respectively of aportion of the bed on an enlarged scale.

Referring to the drawing, a table I of suitable width for the quantityof material t be treated is supported on two longitudinal girders 2, oneat each side. The girders are set at a suitable slope, the left hand endas viewed in Figure 1 being the lower one. At the left hand end onegirder has a bearing housing 3 in which is rotatably mounted one end ofa shaft 4, the other end being similarly mounted in a bearing housing onthe otherY girder 2.

At the right hand end each girder has another bearing housing 5, inwhich is rotatably mounted one end of a shaft 6. All the bearings are ofthe solid rubber type.

Just inside each bearing 3 a link 1 is keyed to the shaft 4 and is keyedat its lower end to a shaft 8, which is mounted at each end by a solidrubber bearing in a, housing 9 fixed to the stationary framework I0 ofthe apparatus. Similarly a link II is keyed to the shaft 6 just insideeach bearing and is keyed at its lower end to av-shaft I2, which ismounted at each end by a solid rubber bearing in a housing I3 xed to theframework I0.

The links 1 and II slope as shown, but the links II are more nearlyupright than the links 1, so that the vertical component of the tablemovement is less at the right hand or higher end than at the left. Thetwo links 1 are united `by a plate I4 and the two links II by a plate I5to ensure that there shall be no lateral oscillation of the table I.

To' provide for the reciprocation of the table, the links `1 Aareextended upwards beyond the bearings 3, each carrying a short length ofshaft I5 to which an eccentric strap I1 is linked by a solid 'rubberbearing. The two eccentrics are mounted on a shaft I8 journalled inbearings I9 on the framework I0. A pulley 20 on the shaft I8 is ldrivenfrom any suitable source of power. The links 'I have extensions 2| topress on springs 22 supported by their lower ends on the framework I0 toeconomise in driving power.

The bearings I9 can be adjusted in a left and right direction to adjustthe slope of the table by a small amount. The slope is varied by thisadjustment because the links 1 are shorter than the links I I betweenshaft centres.

The'surface of the table is of a serrated section with steep fronts 23facing to the right as shown inl-Figure 2. Perforations 24 as shown inFigure 3 are provided in the table surface. The perforations arearranged in transverse rows at equal spacings, each alternate row beingat the bottom of a serration. The lower side of the table is enclosed bya casing 25 connected by flexible material 26 such as canvas to a xedcasing 21, which is supplied with clean air at low pressure from a fan(not shown).

It has been found advisable to regulate the current of air passingthrough the bed of material near the ends, and for this purpose bailles28, 28 project downwards from the table surface `to form airA chambers.Each of the five air chambers shown-has a buttery valve 29 to regulatethe vposition by means of a quadrant 49.

air flow. No such regulation is required ai; the central portion of thetable.

The table has side walls 30 to prevent the material from falling off thesides. A weir 3I is provided at the left hand end of the table tomaintain a suitable depth of material. The height of the Weir can beadjusted by means of a rack `32 and pinion 33 at veach `.end,.a handlever 34 being provided for rotatingthe pinion shaft. The Weir 3l islocked in its adjusted The clean coal is discharged by a chute 35 intoanother chute 36.

At the upper end the table is unperforated from the highest baille 28 tothe end, and here there is a sloping Weir 31 set to give an easy glideangle for the shale. The weir 31 is adjustable in height by means of arack 38 and pinion 39 at each end, the pinions 39 being mounted on acommon shaft, which can be rotated by a hand lever 40 and locked inadjusted position by means of a quadrant 50. The shale falling over thetop of the weir 31 is discharged into a chute 4I.

The raw coal is fed into a stationary hopper 42 of which the dischargeend is in close proximity to a plate 43 hinged at its left hand end. Theplate 43 is supported on a structure 44 attached to the girders 2 so asto participate in the vibration imparted to the latter. As a result thecoal feedis only in operation while the apparatus is working, and noseparate device is required to stop the feed when shutting down. Theplate 43 is hinged to adjust the rate of feed.

From the plate 43 the `coal falls in succession on to a series of plates45, 45 and then onto a corrugated plate 46, by which it is distributedover the whole width of the table. The plates 43, 45and 46 are enclosedin a casing 41.from which air for dedusting is drawn through a ilexibleconnection 48 by a fan (not shown). If dedusting is not required, thecasing 41 is omitted andthe corrugated plate 46 4is extendedup to theplate 43, the plates 45 being omitted, since their sole function is toprovide a coal cascade through which dedusting air can be drawn.

The upper side of the table is left open, as practically no dust isvproduced in the process of cleaning. The operator can see at any timehow the apparatus is working and can at once make any .adjustments whichhe may deem advisable. The air pressure does not need to be high, infact it should konly be sufficient in conjunction with the tablevibration to maintain fluidity of the bed of coal.

In operation the raw coal is first screened into suitable ranges ofparticle size, and each fraction is treated on a separatetable. Asuitable grading may be into six sizes, 1% to in", 1% to B/Bl 1%', lllglr lill S/l sie to 0, but it is advisable to de-dust the smallest size.

The more thorough separation achieved by means of the invention makes itpossible to reduce the active length of the table to about six feet,which further conduces to economy in rst cost vand lin operating power.As already mentioned above, a very low vair pressure is sufficient, andthis again represents a saving in power over existing apparatus for thesame purpose.

What I claim is:

Apparatus for the dry separation of minerals comprisingga slopingperforated table, air supply means lon the underside of the table,v afixed supporting structure for the table, links pivoted on thesupporting structure and on' the table near the lower end thereof andsloping upwards towards the lower end of the table, links pivoted on thesupporting structure and on the table near the upper end thereof andsloping upwards towards the lower end of the table but with lessdeviation from the vertical than the mst-mentioned links, the said linksconstituting the sole support of the table from the supportingstructure, said second mentioned links being longer than saidmst-mentioned links between pivot centres, an eccentric having its straplinked to the table and its sheave driven by a source of power, andmeans for adjusting the position of the eccentric sheave to vary theslope of the table.

G. E. SHAWCROSS.

REFERENCES CI'rE The following references are of record in the le ofthis patent:

UNITED STATES PATENTS

